Fixed Bug 1970. When resizing the plot data the existing data was destroy
before the GUI had been notified of the reallocation. This created a window
of time in which the GUI might access invalid data. The deletion is now
postponed till the GUI has been notified.
Fixed Bug 1698. When initializing a plot the second time we use the same
procedure as when it is created.
Improved loading of plots with a large number of curves into the plot
widget.
Fixed Bug 1969. For a new plot the values for the curve specification are
reset to defaults.